Interstellar Medium and Plasmas

published on 8 July 2014, updated on 9 May 2017 at 11:43

What processes drive the evolution of interstellar matter in the Milky Way and in other galaxies ? What roles do the turbulence, the magnetic field, the cosmic rays, and the radiation field play in this evolution ? Those fundamental questions for modern Astrophysics now appear at many spatial scales and for a great variety of environments : from the galactic scales where the diffuse gas collapse to form the precursors of new stars ; down to the scale of proto-planetary disks where the central star strongly interacts with the surrounding matter ; and even in the stars themselves where the transport mechanisms are still unknown. To study all these astronomical objects, the group « Interstellar Medium and Plasmas » of the LERMA combine theoretical works, numerical modeling, 3D simulations, and observations of interstellar environments at high spectral and angular resolutions.

On the observational side, our group is specialized in the treatment and the analysis of the data obtained with the most advanced space and ground-based observatories. Our expertise is particularly strong in the infrared and sub-millimeter domains which reveal the emission of atoms, molecules and interstellar dust. We have therefore been deeply involved in the recent successes and findings of Herschel and Planck space observatories, which we now follow up by collecting data with the new generation of instruments (in particular, APEX, ALMA, and soon NOEMA).

On the numerical side, the codes developed in our group are internationally renowned as state-of-the-art tools for the analysis of interstellar matter and the interpretation of observational data. Our expertise extends from the conception of 3D numerical simulations of magnetohydrodynamics, which we run using high-level computational capacities (e.g. PRACE, MesoPSL), to the development of advanced numerical models. The strength of those models, which we provide to the community through the ISM and jets platform, is to solve a great number of microphysical processes at play in the interstellar medium, with prescriptions based on the results of laboratory experiments and theoretical studies which are partly performed in our laboratory.

Interstellar medium and Plasmas

Interstellar Medium and Plasmas

Séminaires à venir

Vendredi 22 mars 2019, 14h00

Salle de l'atelier, Paris

New Planckian quantum phase of the Universe before Inflation: Its present day and Dark Energy implications

Sanchez, Norma

LERMA

résumé :

The physical history of the Universe is completed by including the quantum planckian and super-planckian phase before Inflation in the Standard Model of the Universe in agreement with observations. In the absence of a complete quantum theory of gravity, we start from quantum physics and its foundational milestone: the universal classical-quantum (or wave-particle) duality, which we extend to gravity and the Planck domain. A new quantum precursor phase of the Universe appears beyond the Planck scale. Relevant cosmological examples as the Cosmic Microwave Background, Inflation and Dark Energy have their precursors in this era. A whole unifying picture for the Universe epochs and their quantum precursors emerges with the cosmological constant as the vacuum energy, entropy and temperature of the Universe, clarifying the so called cosmological constant problem which once more in its rich history needed to be revised. The consequences for the deep universe surveys, and missions like Euclid will be outlined.

Vendredi 5 avril 2019, 14h00

Salle de l'atelier, Paris

The magnetized interstellar medium in the Galaxy through Faraday tomography of the radio sky

Andrea BRACCO

ENS

résumé :

The study of the diffuse Galactic interstellar medium (ISM) is both a
waypoint to investigate the processes that turn gas into stars and to
account for foreground contaminations in modern high-precision
cosmological probes of the Universe.

New structures in the diffuse ionized and magnetized ISM have been
recently observed through Faraday tomography of polarization data at low
radio frequencies. Although the physical origin of these structures
remains uncertain, interesting correlations with tracers of neutral ISM,
such as atomic hydrogen lines and interstellar dust polarization, have
been found. This opens an observational window on the first stages of
phase transition between diffuse/warm and denser/colder gas under the
presence of magnetic fields, allowing us to constrain their role in
structure formation in the ISM.

In my talk I will present an overview of the recent findings in the
diffuse Galactic ISM with the LOFAR radio polarization data. I will
highlight the relevance of a thorough statistical description of these
data both for Galactic studies and for modeling their impact as a
foreground to the detection of the atomic hydrogen 21cm hyperfine
transition from the Epoch of Reionization, a key step with the upcoming
Square Kilometre Array (SKA).

According to the largely accepted magnetospheric accretion scenario, classical T Tauri Stars (CTTSs) are young stars that accrete material from their circumstellar disk. The objective of my PhD project is to shed light on the processes governing the physics of the accreting plasma flows, through complete radiation magnetohydrodynamic models. In this talk, I will present the results obtained during my 18 month period in Paris.

First, I will focus on the results obtained from a 3D magnetohydrodynamical (MHD) model of a star-disk system. We simulate the effects of series of flares occurring on the surface of the disk. We observe that each flare produces a hot loops that links the star to the disk; all the loops build up a hot extended corona that irradiates the disk from above. Moreover, the flares trigger overpressure waves that travel through the disk and modify its configuration. Accretion funnels may be triggered by the flaring activity and thus contribute to the mass accretion rate of the star. The accretion columns can be perturbed by the flares. As a result, the streams are highly inhomogeneous, with a complex density structure, and clumped.

Second, I will provide the first assessment of the role of radiation effects on the dynamics and the structure of the impact region of the accreting column onto the stellar surface. In particular, we proved the existence of a radiative precursor in the pre-shock part of the accreting column. To achieve such a result, we have, for the first time, developed a Non Local Thermodynamic Equilibrium (non-LTE) radiation hydrodynamics model, which we implemented in the 3D MHD PLUTO code.”